In the context of many networks, and the Internet, it has become commonplace to transfer data utilizing one or more data packets (at the time of transmission of the data, the data is transformed into one or more data packets for transmission on the network or Internet, the packets generally containing 3 main parts, namely, the header, the payload and the trailer). With the proliferation of the Internet, the Transmission Control Protocol (hereinafter and generally referred to as “TCP”) has become the most widely used networking protocol for the transmission of data packets on the Internet. It is generally understood that TCP ensures that no packets are lost during transmissions by giving each transmitted packet a sequence number, which sequence number is used to make sure that the packets are delivered in the correct order at the receiving end. The TCP module at the receiving end acknowledges the receipt of each packet received and in the event that an acknowledgment is not received by the sender within a reasonable round-trip time (hereinafter “RTT”), the sender's timer will timeout and any lost data packets will then be re-transmitted. In this way, TCP generally provides reliable data transmission. However, these re-transmissions reduce the achievable throughput on any given network system.
In circumstances where the network or Internet transmission has a high RTT (for example where the transmission is over a lengthy distance) or has a high packet loss potential (for example where the transmission is over an earth to satellite link, or is being broadcast or sent by radio or microwave transmission), the need to retransmit packets by way of the TCP significantly lengthens the overall transmission time for a given data transfer.
Furthermore, TCP responds to latency and the resulting round-trip delay between the transmitter and receiver, by reducing the data transmission rate, and thus reducing the achievable data throughput.
An alternative data transfer protocol User Datagram Protocol (hereinafter “UDP”) may be utilized to transfer data across a network or the Internet. In some circumstances, UDP provides extra performance over TCP, for example, as it does not require the sender and receiver to establish a connection before data is transmitted, it does not require acknowledgment and retransmissions of lost packets, and allows the UDP packets to be received in an order that is different from the one in which they were sent. As will be appreciated, this may result in reduced reliability of the data transmission.
It is therefore desirable to have a high speed, high reliability data transfer protocol that works well in circumstances where the network has a high round trip time, and with high packet loss characteristics. It is also desirable to have a reliable data transfer protocol that provides access to a larger portion of the available bandwidth, and which automatically adjusts to network conditions. In addition, it is desirable to have the ability to multicast/broadcast to multiple clients so that all files are transferred at the maximum line speed available for each client.